Acid concentration



.J. ma Anus ET AL.

ACID CONLIENTRATION Original Filed July 1, 1920 VINVIENTORJ E.

A TTORNE V J. B. EIMNAFMfizl a a Original Filed July 1,

5 shejets sl leet" 4 ONCENTHATION ACID E E3! "J briginal Filed July 1,

ATTORNEX may 26,, 192%.-

- .J. B. EDVVARDS'ET AIL.

ACID CONCENTRATION "5 Sheets-Sheet 5 Original Filed Jll1y- ;L, 1920 A1 TTORIVEF Patented May 26, 1925;

UNITED STATES PATENT OFFICE.

JOSEPH n. EnwAnn's, or JERSEY CITY, AND FREDERICK E. EAULKZNER, or BAYONNE,

NEW JERSEY, assreuons or ONE-FOURTH T TIDE WATER OIL contrary, or nAYouNE, NEW JERSEY, A conrona'rrou o NEw JERSEY. f

ACID CONCENTRATION.

Application filed July 1, 1920, Serial No. 393,338. Renewed January 11, 1922. Serial No. 528,559.

To all whom it may concern:

Be it known that we, JOSEPH B. EDWARDS and FREDERICK E. FAULKNER, citizensof the United States, and residents, respectively,

otJersey City, in the county of Hudson and State of New Jersey, and of Bayonne, in the county of Hudson and State 01 New Jersey, have invented new and useful Improvements 'in Acid Concentration, of which the following is a specification.

The invention has to do with the concentration of sulphuric acid and other -liquids of high boiling point, and is constrength, and also freed of theextraneous material. Heretofore, this operation has been very inefficient, and for this and a" number of other reasons has been one of the most troublesome problems of thein The fuel cost has been unduly high dustry. and the recovery ofacid of the desired strength unduly low, the apparatus has been especially subject to wear and destruction, necessitating frequent costly replacements,

and the'liberated fumes havebeena serious nuisance to the neighborhood and a cause of damage, besides representing a loss in acid. The nature of the vapors and fixed gases has rendered the work unpleasant and injurious to those engaged; and where it has been i'iecessary to erect a. building and stack to control and deliver them to the upper atmosphere, the difficulties of the workers have been increased and the building itself has deteriorated rapidly owing to the corrosive and charring after.

action of the vapors. There has been some variety in the manner of conducting the operation and in the apparatus employed, but none of them, as far as we are'awar e, has effected any radical and general improvement in respect to the drawbacks with which the art has been familiar.

The object of this invention is to provide an acid-concentrating and purifying apparatus and method, and parts thereof, Whereby, among others, the following advantages are realized: large reduction in fuel cost with'large increase in recovery,and possibility of operating economically u on more dilute acid than heretofore, low rst'cost, low. maintenance charges, mfrequency and simplicity of repairs and replacements and ease of overhauling, avoidance of prolonged shut-downs, minimum laborrequlrement for operation, and practical elimination of the;

fume difficulty, making it possible to run in the open, in any neighborhood without a building 'or stack, and rendering the conditions of labor unobjectionable. These re sults are accomplished by'means of, certainnovel apparatus novel to the art and by combinations of apparatus, andby the methodof treatment therewith involved, all as will be more particularly described herein-1 Briefly stated, the weak acid, in continus ous gravity flow, is partially evaporated in open receptacles, and the concentration then completed in a, special iron pipe evaporator. This closed evaporator constituting an important feature of the invention, comprises a generally horizontalgroup of pipes of substantial size and thickness made of material such as high-silicon cast-iron, resistant to the action of the concentrated acid, said pipes being dis osed across the interior of a urnace cham er, with their ends \projecting through the walls to receive external connections whereby they are placed insinuous'series, there being an inlet connection from the open receptacles to the iirst pipe ofthe series, and an outlet connection from the last pipe forthe concentrated acid. the

whole being constituted and arranged so that the acid flows evenly by gravity through the serpentine channel, partially filling the pipes and leaving a gas and vapor chamber in their upper parts, from which latter the vapors and gases are taken'oft" for disposal at certain of the external conncctions, while being prevented from escaping at the concentrated acid outlet. Prior to our invention the form. of iron evaporater which has been most, generally used in the concentration ofthis acid has been the primitive covered pan type, consisting "of a large, heavy, shallow oblong body having a flange around its top, and a similar flat-- dle, and owing to their weaknesses cause the plant-to be out of commission a substantial part of, the time. have been generally deemed the'most practical piece of apparatus for the purpose. Our closed evaporator, in' contrast, costs less in the first instance, is infinitely longerwearing, in case of failure at one point only that pipe section is affected and can be quickly and easily withdrawn and another substituted, and the life of theisections can be prolonged by detaching the external con nections at comparatively long intervalsand turning them so that fresh portions of the surface are presented; furthermore, the efiiciency as a concentrator in respectato fuel consumption and output and the reduction in fixed gasesand acid vapors is very much higher.

The open receptacles are of two kinds, the first group consisting of open leadpans fired beneath, and the second, between the lead pans and the iron pipe evaporator, of. castiron basins arranged in cascades, the material of these basins beingsimilar to that of the pipes. The use of open lead pans is well known in the art, nor do we claim merely the use of cascades, but by the combination of the lead pans, 1ron cascades, and

iron pipe evaporator, connected so that the acid flows through them in the order named, a new result is obtained, namely that the acid can be evaporated in the open from a low'strength, around 30 Baum, to a comparatively high concentration, around 60 Baum, only the last six degrees, or thereabouts, of concentration being efiected in the closed evaporator, and yet without the liberation of a material quantity of acid fume and with the least deterioration of the apparatus in the several stages. Thus, .the

Yet on the whole they first stage of concentration in the lead pans can be from about 30 Baum to about 45 Baum, and the second in the 11011 cascades from about 453- Baum to about GO 'Baum, However, it will be understood that these figures are intended as illustrative and that the different rangesa're subject to variation without essentially altering the principle, theimportant elements being that it is practicable to accomplish a much greater part of the concentration in open receptacles than previously, that the loss ii fixed gases is reduced, and that the destructive effect on the apparatus as a whole is greatly lessened.

The advantages of the invention can be realized in art by conducting the acid direct from he lead pans to the iron pipe evaporator, the cascades being omitted, but in that event the evaporator must be made more extensive, seats to take in approximately the concentration range of both the 'cascades and the evaporator of the preferred embodiment.

The open receptacles 'are advantageously arranged over twin heating flues leading from the iron pipe evaporator furnace chamber, which latter is equipped with burners which supply the heat for the whole plant, the combuston gases surrendering heat first to the pipes'and then flowing under the. cas-' cades and finally beneath the lead pans. In this manner the fuel consumption can be made exceptionally low.

The lead pans are disposed in a special grouping with cross-gutters connecting them,

whereby any pan requiring-attention can be readily bridged out of circuit, so that work can be done upon it without interrupting the operation of the plant. Agitating jets, of air or steam, are made use of in these pans to effect an important improven'ient, by preventing lodgment of'carbonaceous matter on the bottom, which causes pitting and ulti- -mate destruction, bringing the same to the surface and-directing it to a region where it can be conveniently,removed by skimming. These and other features of the invention will become apparent as the specification N Fig. i is an enlarged vertical-transverse 7 section through a pair of the lead-pans;

Fig. is a similar view, illustrating a modificatlon;

Fig. 6 1s an enlarged front elevation of one of the externalconnections of the so-called pipe evaporator constituting the final concentrator; 1

Fig. 7 is a vertical section on the line 7- 7 of Fig. 6

Fig. 8 IS an enlarged vertical longitudinal section through the terminal portion of the pipe evaporator;

Fig. 9 is a cross-sectional view corresponding to Fig. 8, the section being taken through the pipe 31; and

Fig. 10 is an enlarged vertical transverse section through the cascades.

1 is a rectangular brick furnace chamber having oil-burners 2 at oneend. From the opposite end of the chamber and in open communication therewith extend twin, parallel lines 3, 3?, inclining somewhat upward from the horizontal,-and their halves more or less adjacent the furnace chamber having a greater inclination than the remote portions. carry oil the combustion gases.

Open oblong lead pans5, 5, 5, 5 are arranged over the tops of the outer parts of the fines 3 so that their bottoms are heated by the flame gases flowing therein, the bottoms being protected from direct action of the ga by cast-iron plates 5", These gases having already given'up a large partof their heat, the lead pans are only moderately heated.- The pans 5 and 5 are over the flue 3 and the pans 5, and 5 over the flue 3.' In operation the weak acid to be concentrated continuously enters the pan' 5 at the outer side and near one end thereof, through a supply conduit 6, flows through this pan, then across to the pan 5, through this pan and then to the pan 5", and thr back across to the pan 5. The connec are made by cross-gutters 7, 7 between tne opposed sides of the pans 5, 5 and 5", 5, respectively, and a longitudinal gutter 7" at the outer sides of the pans 5, 5", having transverse outlet and inlet ends 7, 7 opening through said sides. The supply conduit 6, cross-gutter? and outlet 7 are in transverse ahnement, as are also the inlet 7", cross-gutter 7 and an outlet 7 from the outer side of pan 5 "so that any one of the pans can be cut out by placing across a temporary bridge. The pans are set. at successive slightly lower levels through the series 5, 5, 5", 5, for purposes of flow, and circulation throughout the pans is promoted by longitudinal fins 8 therein extending from the end of each adjacent its inlet and outlet to within a short distance of the opposite end.

Stacks 4 at the farends of the titles trance to a sloping trough 9 which extends.

beyond the end of the pan and then across, the cross portion of the trough having two outlets 10. These outlets deliver the now partially concentrated acid to the upper ends of two cascades 11, 11 over the more steepl descending portions of the lines 3, 3". ach of said cascades consists of a stepped series. of open basins 12 of highsilicoin cast-iron, capable of resisting the action of the acid as it becomes more concentrated, as well as the higher heat encountered at this region. The said basins are preferably of rounded oblong form with curved bottoms, arranged crosswise in the series, each havin 'a spout 13 11 the upper part of its forward wall, throu h which the acid overflows into the top of the basin next below, the spgutsbeing arranged alternate lytoward opposite sides of the series.

The bottoms of the basins are exposed to the flame gases in the hues; and each basin is shown as havinga' transverse inclined circulating tube .14 of similar material passing acrossthe'flue below the basin. The ends of each of said tubes extend outward through openings in the side \WilllS of the sis These tubes are useful asthey provide additional, readilyreplaceable heating surfaces in the fire, making "the heating more efiicient and vsaving the bottoms of the basins. The tubesare not, however, essentialfand may be omitted. Similar tubes might also be used in connection with the open lead pans. as indicated in Fig. 5, where like parts are designated with the. same reference numerals with super-character a. i

From the spouts of the lowermost basins of the two cascades, adjacent the furnace chamber '1, the acid,v now .further concentrated, flows into funnel entrances 21. of a conduit 22, which passes with suitable pitch atone side of the chamber 1, and is connected to one end of a relatively large pipe 23 forming the first member of. a generally horizontal group of such pipes extending across the interior. of the chamber 1. This part of the apparatus constitutes a closed evaporator. In it the series of pipes may progress, "for convenience, away from the burners, as shown, or. vice versa.

leadislide regulating valve 24 in the conduit 22 controls the supply of acid to the closed evaporator and enables it to be cut oif altogether, and a branch 25 behind this point, containing a valve 26, enables part or all of the-flow from the open lead pans andiron cascades to be diverted to a lead-lined receiving tank 27.

The pipes 23 are supported in openings in the side walls of the furnace chamber and in a central Wall 28, their ends projecting outward and being furnished with flanges 29. The pipes are generally horizontal and parallel, though preferably slightly pitched al-;

ternately in reverse directions, and each succeeding pipe is set slightlye lo wer than the preceding one oftheseries, assess in Fig. 2", in order that there may be a steady quiet flow through the closed evaporator. Their adjacent ends, with the exception of the inlet end of the first pipe and the outlet end of the last pipe, are joined by external sediment-box connections 30 in such fashion as to form a sinuous or zigzag gravity passage. The pipes are made of the acid-resisting high-silicon cast-iron, of which the cascades are also composed, and should be of moderately large diameter and have relatively The outlet end of the last pipe of the series, which as shown is the pipe farthest from the burners and nearest the cascades, has an external outlet connection 30 applied to its flange. This connection is relatively large, or the samediameter as the pipe, and to its outer end is secured eccentrically'a small connection 31-, setsubstantially on a bottom level therewith, the-con-' nection 31 delivering into a suitable sediment chamber 32. Between the proximate flanges 33, 34 of said connections and bolted therewith is a disk 35 of the acid-resisting metal, having a restricted opening 36 toward the bottom. This opening regulates the outflow of concentrated acid from the pipes of the evaporator and in connection with the means of supply and the'drop through the evaporator determines a depth of acid in the pipes only partially filling them, as seen in. Fig. 8, leaving a vapor and gas space 37 in their upper halves, which like the. liquid chanml is continuous throughout the evaporator by virtue of the connections 30. The disk 35 with its opening toward the bottom also constitutes a gas trap, presenting a solid wall across the end of the gas space of the evaporator so that the gases and vapors are prevented from passing out with the concentrated acid. The connection 30 also serves .as a receptacle for a recording thermometer 65.

' From the sediment settling chamber 32, the concentrated acid passes through a pipe 38to a cooler coil 39 and thence to a lead lined running tank 40, which is the end of this partof the system.

The gases and vapors are taken off from the common vapor space of the evaporator at one or more points in the external connections. It has been found suflicient to connect vapor outlets 41 with the terminal connection 30 and one ,of the intermediate connections 30 at the same side. Said outlets extend vertically upward and have a cross-connection 42, from which a Vapor line 43 extends to a condenser 44, wherein the thermal conditions are such as to condense out most of the vaporized acid which is carried over. The condensate is weak acid, and is conducted away from one or more gas traps 45 connected beneath the condenser coil, through a return pipe 46, having a testing tank 47 therein, to a suitable portion of the system, preferably one of the open leadans.

P The uncondensed gases pass on from the condenser through a line 48, having valved steam and water connections 49, 50. Either or both of these agencies can be employed to take up the gases and carry them along. From the water connection the said line extends downward to a rotary pump 51, the function of which is to agitate the fluid and promote absorption. At the other side of the pump the line 48 finally leads to a sewer. A separator 52 may be placed inthis portion of the line, and an absorbent chamber 53 in the portion near the condenser. In the operation of the system a slight suction is maintained on the piping and condenser, amounting approximately to one-quarter of an inch of water column.

; The connections 30 between the pipes of the back by annular bosses 55 to bear against the flanges 29, the bosses being perforated to receive securing bolts 56, passing also through the flanges. In the top of the box is an opening 57 adapted for one of the vapor outlets 41, the connections being preferably made all alike and interchangeable, so that the vapors and gases can be taken off from any or any number of them, the openings 57 which are not so used being closed. The flooi' of the box is substantially below the bottoms of the inlet and outlet openings 54 in the rear wall, whereby a sediment'trap is formed where the stream is bafiied in passing from one pipe to another, causing any material still' carried by the acid to be deposited at these regions rather than in the pipes.

openings 66 in front of the pipes, which extend down to the floor and are covered by removable cover plates 58 secured by screws 59. Upon taking oil this cover accumulations in the boxes can be removed, and the pipes themselves can also be. cleaned.

The weak acid as it comes to the lead pans 5, etc, contains a large-amount of carbona. ceous impurities, and as is common practice these open receptaclesare utilized for skimming oli' the matter rising to the top. A certain proportion of the impurities, however, settle to the bottom and sink into the lead, causing pitting, and have to be dug out from time to time to prevent perforation, while the pan is temporarily out of commission. In order to avoid this wear and to reduce the labor item we employ forced jets of air or steam, or other fluid, in the pans, the same being delivered through suitably supported nozzles 60 plunging beneath the surface of the acid and connected with conduits 61 leading from a source of supply of the fluid under pressure. The nozzles may be variously arranged to create currents over the bottom of the pans preventing settling of the impurities and favoring their movement to the surface, where they will be removed. The nozzles are also advantageously arranged as indicated more or less parallel with the bottom or at an in clination thereto so as to drive the material to an end or corner where it can be conveniently taken ofi'.

In heating the acid containing oily impurities, more or less reduction takes place, carbon compounds being oxidized at the expense of the sulfuric acid with production" of $0,. In flowing weak sludge acid as shallow layers is hot pans exposed to the .ttll, the air exercises anoxidizmg influence and, to that extent, lessens the loss of acid by reduction to S0,, of the carbon compounds; and in agitating with air, useful oxidation also occurs.

Such agitation is also a material factor in concentration, by causing circulation, bringing the various parts .of the liquid into contact with the heating surfaces and with the air, and by producing evaporation within the liquid. The air or gaseous fluid, if not already heated, when delivered near the bot toms of the pans becomes highly heated and cap-able of taking up much water vapor as it bubbles upward through the liquid.

To summarize caused to pass by enough of the diluting liquid is evaporated to bring the acid from the initial gravity of approximately 30 Baum to. a strength of about i5 Baum. At this stage the. bulk of the carbonaceous impurities are removed by skimming, this operation being, facili- -cascades, being the weak acid is first gravity in circuitous course through the open lead pans. Here tated by the jets, which a of adhering clots. The stream next divides and passes step biyl step down \the double iron rther heated therein, and concentrated to a strength \cr about, 60

lsdperform theimportant function of keeping the bottom free Baum at the foot. Impurities may alsobe skimmed in the cascades.

In the third stage, the divided stream reunites and still flowing by gravity pursues its way through the serpentine channel of -th iron pipe evaporator, wherein it is brought up to' the final required strength of 66 Baum. The concentrated acid flows out past the gas trap to the cooler and running tank. The vapors and gases are conducted away from the external connections of the pipes, the part worth returning to the systemis condensed, and the remainder is absorbed in water or steam, mechanically mixed, and

delivered to the sewer. The progress of the operation as a whole is so ordered and the,

relation between the stages is such that the concentration though carried but largely in accessible open receptacles generates a minimum of acid fumes, and such as areproduced are confined practicall altogether'to the closed stage. Here the oss in acid ivaporsand'fixed gasesis slight, .owing i the natureflof the heating, the influenceof the pipe walls and to the fact that the whole of the acid in the closed evaporator is in continuous, even'flow, without dead areas over the fire. Hence all portions of the acid enteri the pipe evaporator remain therein for e same period and are subjected to the same heating, and are consequently brought to the desired concentration quickly with the least consumption of fuel, and without overheating of any part so as to generate an excessive proportion of fumes. or gases. Such acid vapors as aredriven oif are largely condensed and returned to the system. A controlling factor throughout is the gradual manner in which the process is carried on. vForcingat any point gives rise to quantities of acid vapors and fixed gases.

In the final stages of concentration, in getting rid of water it is necessaryto carry the temperature to a point 'where'sulfuric 'acid also vol atili zes to a. substantial extent. 111 the present procem this final concentration is effected intransit on whatare practically flowing films or thin liquid layers with an extensive evaporation su ace,- thereby permitting free evolution of water por, while the acid vapors which are inva evitably formed also cannot escape. .In handlin sludge acid, for which the present system is particularly adapted, therev is no opportunity aiforded for the deposition of any separated carbonaceous matter on heating surfaces.- p

What we claim as new is: a

1; Apparatus for concentrating the weak acid ofpetroleum refining, comprising a group of open lead-pans, a cascade of iron basins, and a closed evaporator comprising a furnace chamber and a substantially horizontal collection of iron pipes in the furnace chamber with their ends passing through the walls, andexternal connections placing tl em in sinuous series, the whole being--connected 'andnarranged for continu-' collection of iron pipes in the furnace chamher with their ends passing through the Walls, and external connections placingfthem in slnuous series, there being a connection whereby the acid partially concentrated in the open receptacles fiows to the first of said series of pipes, and means for disposing of the vapors and gases given off therein.

3. Apparatus for concentrating the weak acid of petroleum refining, comprising a furnace chamber provided with burners, and

flues extending therefrom, open evaporating receptacles connected in series over said flues, said receptacles comprising a group of open lead pans and cascades of iron basins to which the acid passes from the lead, pans, and a substantially horizontal collection of iron pipes in the furnace chamber with their ends passing through the walls, and external connections placing them in sinuous series, there being a connection whereby the acid partially concentrated in the open receptacles flows to the first of said series of pipes, and means for disposing of the vapors and gases given off therein.

4. Apparatus for concentrating the weak acid of petroleum refining, comprising a' furnace chamber provided with burners,

and parallel flues extending therefrom, a

nace chamber with their .ends passing through the walls and external connections placing them in sinuous series, means whereby the partially concentrated acid from the pans reaches the first of said series of pipes, and an offtake and condensing system for the vapors and gases produced therein.

5. Apparatus for concentrating the weak acid of petroleum refining, comprising a furnace chamber provided with burners, and parallel flues extending therefrom, a group of open lead-pans over the outer parts of said flues, with cross-connections whereof the flues, with a connection from the last of the open pan series to the head basins of-the cascades, and a' closed evaporator comprising a collection of .ironpipes in the furnace chamber connected in sinuous series, with a connection from the foot basins of the cascades to the first pipe of said series.

6. In apparatus for concentrating the weak acid of petroleum refining, a furnace chamber a substantially horizontal collection of high-silicon cast-iron. pipes in the furnace chamber, sediment boxes connecting their projecting ends in sinuous series, means whereby the acid is caused to pass in steady flow through said pipes and sediment boxes, depositing its impurities in the latter, means for taking off vapors and gases from one or more of the sediment boxes, and means for conducting away the concentrated acid without escape of the gases.

7. An acid-concentrating evaporator comprising a furnace chamber, and a substantially. horizontal group of iron pipes in said chamber with their ends passing through the walls of the chamber, and external removable connections applied to said ends comprising connections placing the pipes insinuous series, and inlet and outlet connecti-ons for the relatively weak and concentrated acid respectively applied to the first and last pipes of the series, the wholebeingconstituted and arranged for continuous flow through the serpentine channel, partially filling the pipes and connections and providing a gas and vapor chamber in their upper parts, and means for conducting off the vapors and gases from certain of the external connections.

8. In an acid-concentrating evaporator as set forth in claim 7, the form of the external connections betweenthe ends of the pipesco-mprising boxes, each having a pair of openings in the back with seats for the flanged pipe ends, their bottoms at a distance below said pipe openings, and a removable front cover.

9. In an acid-concentrating evaporator of 1 the character set forth in claim 7, the combination with the last pipe of the series, and an outflow pipe of smaller diameter set at approximately the bottom level of the evaporator pipe, of a gas trap and flow restriction comprising a disk interposed between the proximate ends of said pipes and having an opening in its lower portion.

10. In an acid-concentrating apparatus, the combination of a closed evaporator of the character set forth in claim 7, a cooler for the concentrated acid, a gas trap at the liquid outlet from the closed evaporator, and a sediment chamber between the gas trap and the cooler.

- 11. The method of treating sludge acids or separated sludge acids which consistsin heating and agitating a body of'the acid thereby effecting a partial concentration of the sameand in then heating a body of the partially concentrated acid without agi-- tation effecting: a' further concentration 3 thereof.

12. The method .of treating sludgeacids or separated sludge acids which consists-in heating and agitating a'body of the acid of about' degrees Baum thereby effecting a partial concentration of the same up 'to.

about to degrees Baum and in then heating a body of the partially concentrated acid without agitation effecting a concen-- tration thereof 'to about 66 degrees Baum."

13. The method of treating sludge acids or separated sludge acids which consists in bubbling air or gases through a'body o'fthe heated acid thereby effecting a partial concentration thereof and in then heating a body of the partially concentrated acid without agitation effecting a further concentration thereof. a r

14. The method of treatingsludge acids or separated sludge acids-which consists in bubbling air or gases through a body of,

the heated acid of about 30 degrees Baum thereby effecting a partial concentration thereof. up to about 45 to 60 degrees Baum and in then heating a body of the partially concentrated acid Without agitation, efi'ects ing a concentration thereof up toabout 66 degrees Baumc. 15. The method of treatingsludge acids or separated sludge acids which consists in heating and agitating a weak sludge acid' thereby effecting a partial, concentrationthereof andin then heating the partially concentrated acid at a higher temperature and close'to the boiling point of the acid for eflecting a further concentration thereof.

16. The method of treating sludge acids or separated sludge acids which consists in heating and agitating a weak sludge acid thereby effecting a partial concentration thereof, in then heating the partially concentrated acid without agitation at a higher temperature. and in then heating the so treated acid to eflect further concentration thereof.

17. The method of treating sludge acids or separated sludge acids which consists in heating and agitating a weak sludge acid thereby effecting a partial concentration thereof and in then heating the partially concentrated acid without agitation at a higher temperature and substantially without concentrating the same and in then heating the so treated acid to effect further concicntration thereof.

18. The method of treating. sludge acids or separated sludge acids Which consists in heating and agitating a body of Weak sludge acid thereby effecting a "partial concentration thereof, in thenheating a body of the partially concentrated acid Without agitation' at a higher temperature andin then heating the so treated acid to effect further concentration thereof. I

19. The methodof treating sludge acids or separated sludge acids which -=consists in heating and agitating aweak sludge acid to effect a partial'concentration thereof to from about 45 to 60 degrees Baum, in then heating the partially concentrated acid without agitation at a higher temperature and in then heating the sotreated acid to effect or separated sludge acids which consists in bubbling air or gases through a body of Weak sludge acid, heating and agitatin the same to effect a partial concentration t ere of, in then heating a body of the partially concentrated acid without agitation and subj stantially without concentrating tlfe same and in-then heating the so treated acid to. effect further concentrationthereof.

22. The steps in the method of treating sludge acids or separated sludge acidswhich consist in heating and agitating a weal;

sludge acid thereby concentrating the same to an intermediate strengthand-in then heating the said partially concentrated acid .without agitation at a higher temperature.

23. The-steps .in the method of treating sludge acids or separated sludge acids which consist in heating and agitating a body of weak sludge acid thereby concentrating the same to an intermediate strength and in then heating the said partially: concentrated acid without agitation at ahigher-temperature..

24. The steps in the method of treating sludge acids or separated sludge acids which consist in bubbling air or gases through a body of weak sludge heated acid thereby concentrating the same to an intermediate strength and in heating the said partially concentrated acid without agitation at a higher temperature.

JOSEPH B. EDWARDS. FREDERICK a. FAULKNEB, 

